Young women in their childbearing years are the fastest growing group for Type 2 diabetes mellitus (DM). Recent studies suggest that lactation may confer a physiologic protection against diabetes and cardiovascular disease for several years after weaning. However, there is a striking lack of animal or human studies regarding the mechanisms through which lactation might affect chronic disease processes. We propose to examine the associations of lactation duration with levels of insulin resistance, inflammation, lipoproteins, leptin, adiponectin and ghrelin at 3 years postpartum. We will use data and plasma samples from Project Viva, a prospective cohort study of women enrolled during pregnancy and followed for several years postpartum. To our knowledge, this will be the first study of the metabolic impact of lactation in a population-based group of postpartum women. If compelling, the data generated by this grant would form the basis for a new longitudinal cohort with serial postpartum measures of insulin resistance. If this and future studies demonstrate that lactation can reduce the risk of diabetes and its complications, there would be immediate, important, easily implemented clinical implications. We submit this application in response to PA-04-137, which solicits "novel approaches to detect, prevent, or delay the onset of diabetes and its complications". [unreadable] [unreadable] [unreadable]